The present invention relates to an image processing apparatus having an original read unit for reading an image on an original document by a prescan and a copy scan, an image data processing unit for converting original image signals into digital image data signals and then for processing the digital image data signals, and an output unit for outputting processed image data signals.
A digital copying machine converts analog image signals, which are gathered by reading an image on an original document, into digital multi-valued data, and processes the multi-valued data for image quality adjustments, such as granularity, gradation, and definition, thereby reproducing the original image in the form of a mesh-dot image. In a full color digital copying machine, an image on the original is optically read and separated into three color signals B (blue), G (green), and R (red). The color signals B, G and R are color-corrected into recording signals Y (yellow), M (magenta), and C (cyan) of coloring materials, such as toner, ink, ink donor film, or the like. Mesh-dot images of the respective coloring materials are superposed to reproduce a full color original image. Actually, the coloring materials of equal quantities are removed for saving the coloring materials (this process is called an under color removal (UCR)), since the coloring materials of equal quantities make up a nonchromatic image. The color image after undergoing the UCR is reduced in the quantities of coloring materials used. Accordingly, it gives an expression lack of deepness and accordingly is poor in voluminousness on the whole. Since the reproduction of gray and black is contradictive to the reproduction of color of high chroma, simple UCR processing will insufficiently improve the color reproduction performance. For improving the color image of poor voluminousness or for a gray component output, black (K) is generated of which the quantity corresponds to the quantities of coloring materials removed by the UCR process.
As described above, the analog signal is converted into a digital multi-valued data signal, and the digital data signal is used for various processings. The image data signal, taking the digital form, is convenient in executing various types of processings. The digital image data signal is temporarily stored into a memory, and it is read out of the memory when required, for example, when various types of edits are executed, such as data conversion, correction, adjustment, and others. Accordingly, the machine may have many additional functions. To operate the machine, an original document is set and a start button is pushed. Then, the machine prescans the original, and automatically detects the size of the original, and selects a paper of the detected size. Where a magnification percentage is designated, the machine multiplies the detected size by the designated magnification, and selects a paper of the calculated size and copies the image on the paper. To detect the size of the original, the edges of the original must be distinguished from the read image data. To this end, the platen is designed to have the reflectivity different from that of white or to have color, not white. For this reason, the peripheral portion of the paper extended beyond the original, when copied, has an optical density or the color of the platen. By utilizing this feature of the original size detection, the image signals representing the peripheral portion of paper, or the platen, are converted into color signals of white as the texture color of the original.
For a better understanding of the digital color copying machine as mentioned above, the digital color image forming apparatus proposed by Unexamined Japanese Patent Publication (Kokai) Hei-2-70173 and Hei-2-131662 will be described briefly.
FIG. 7 is a block diagram showing the arrangement of the digital color image forming apparatus.
In FIG. 7, an IIT (image input terminal) 100 reads an image on an original by using a CCD sensor, and converts color separated image signals B, G and R into digital image data. An IOT (image output terminal) 115 reproduces a color image through the laser-beam based exposure and developing processes. The blocks ranging from an END conversion module 101 to an IOT interface 110, which are located between the IIT 100 and the IOT 115, make up an image processing system (IPS). In the IPS, the read signals B, G and R are converted into toner recording signals Y, M and C, and additionally K. Every developing cycle, the recording signal corresponding to the developing color is selected and output. In converting the read signals (B, G and R signals) into the recording signals (Y, M, C, and K signals), how to adjust color balance, how to reproduce the colors in accordance with the read characteristic of the IIT and the output characteristic of the IOT, how to adjust the balance of the density and contrast, how to adjust the edge emphasis, blur and Moire, and the like become problematic.
In the IIT 100, the read signals B, G and R are gathered, by a CCD sensor, at density of 16 dots/mm for one pixel, and are output as data of 24 bits (3 colors.times.8 bits; 256 gradations). The CCD sensor of 300 mm long and at the density of 16 dots/mm has B, G and R filters mounted thereon. It is capable of making the scan of 16 lines/mm at the process speed of 190.5 mm/sec. Accordingly, it outputs a read signal of each color at the rate of approximately 15M pixels per second. The IIT 100 logarithmically converts the B, G and R analog signals of pixels, so that the reflectivity data is converted into density data, and further converts the analog signals into digital signals.
The IPS receives the read signals B, G and R, processes the image data signals for improving the reproduction quality of colors, gradation, definition, and the like, selects recording signals of the developing process colors from the recording signals Y, M, C, and K, converts the signals into on/off signals, and outputs them to the IOT 115. The IPS, as shown in FIG. 7, is comprised of an END (equivalent neutral density) conversion module 101 for adjusting (converting) the image signals into gray-balanced color signals, a color masking module 102 for converting the read signals B, G and R into recording signals corresponding to the quantities of toners Y, M, and C by matrix operating the read signals, a document size detecting module 103 for detecting the document size in a prescan mode and for erasing (frame-erasing) the platen color in a read scan mode, a color change module 104 for changing the color, which is designated in a specific area, according to an area signal input from an area image control module, an UCR & black generating module 105 which generates a proper quantity of black K and removes the equal quantities of the colors Y, M, and C according to the quantity of generated black so as not to cause color impurity, and gates the signals after the K signal and the Y, M, and C signals are subjected to the under color removal process according to the signals of a monocolor mode and a 4-full color mode, a spatial filter 106 having the functions for blur removal and for Moire removal, a TRC (tone reproduction control) module 107 having various functions for reproduction quality improvement, such as density adjustment, contrast adjustment, negative/positive inversion, and color balance adjustment, an enlargement/reduction processing module 108 for enlarging and reducing the image size in the fast scan direction, a screen generator 109 for converting tone toner signals of process colors into on/off or binary-coded toner signals, an IOT interface module 110, an area image control module 111 including an area generator circuit and a switch matrix, and an edit control module including an area command memory 112, a color palette video switch circuit 113, a font buffer 114, and the like.
In the digital color image forming apparatus described above, the original frame-erasure processing is performed in the document size detecting module 103 The outline of it will be given hereunder (see Unexamined Japanese Patent Publication (Kokai) Hei-2-131662).
The original frame-erasure is the processing to erase the frame of an original document, viz., to convert the signals indicative of the platen cover into white signals. In the frame erasure processing, during a copy cycle of each developing color, the machine clears the read data of the platen cover portion into the white signal, while recognizing colors. At the same time, the machine allows the image data of the original document to be output as intact. Accordingly, the frame erasure processing requires a color detection. Where attempt is made to erase the frame of the original by using the output signal of a spatial filter selected by the developing color, one encounters such a problem that the edge of the original cannot be detected. It is for this reason that the image data before the developing color being selected and the processings of the color change, UCR and the like being carried out is used for the frame erasure processing. Specifically, when the input image data of Y, M, and C are below the threshold value, it is decided that the image data is that of the original document, and the leading and trailing edges of the data signals are detected. At the n-th line, the count at that time is latched by using the leading and trailing edge signals, is operated, and the operated values are used as the values indicative of the area within the original. At the subsequent (n+1)th line, the image area signal is generated using the operated values. On the basis of the original area signal, the signals indicative of the area outside the original are converted to white data signals.
In erasing the frame by using the original size detecting module, erasure is made of only the shade of the platen back outside the original. In the case of the repeat processing, for example, the harmful influence by the frame erasure becomes actual. Furthermore, inputs and outputs are required for Yellow, Magenta, and Cyan of coloring material, respectively. Therefore, the processing circuit becomes a large scale, and a number of input/output signals becomes a large number.
FIG. 8 shows explanatory diagrams for explaining the harmful influence caused by the conventional frame-erasure processing. In the conventional frame-erasure processing using the original size detecting module, when the copy is carried out in a repeat mode, spaces caused by the frame erasure process appear, every time the image is repeated, in a series of images, as shown in FIG. 8A. In other words, it is impossible to form a series of repeated images continuously arranged as shown in FIG. 8B. In the conventional frame erasure technique, after the edge of the original is detected, a fixed area extended outside the detected edge of the original is erased. In other words, the erased area cannot flexibly be changed as desired. Accordingly, in a rectangular shape as shown in FIG. 8D, the frame erasure is impossible. The resultant image is as shown in FIG. 8C.